1. Technical Field of the Invention
This invention relates to a method for the purification of a mixture of alkyl amines. More particularly, this invention relates to a method for the purification of a mixture of alkyl amines prepared by the reaction of a lower aliphatic alcohol containing 1 to 4 carbon atoms with ammonia. When ammonia is reacted with the lower aliphatic alcohol, the product of the reaction is mixture of the mono-, di- and triamine derivatives of the alkanol. It is conventional practice to separate the mixture by azeotropic or extractive distillation in order to provide purified compounds.
In accordance with the present invention, a process is provided for the separation and purification of a mixture of mono-, di- and trialkylamines through the provision of a process relying upon reversible chemical reactions. In accordance with the present invention, a formyldialkanolamine selected from the group consisting of formyldiethanolamine, formyl aminoethylethanolamine and formyl 2-(2-aminoethylamino)-ethanol is added to a mixture of alkyl amines to form a reaction mixture which is heated at a temperature of about 120.degree. to about 160.degree. C. and at a pressure of from about 500 to about 3,000 psig to substantially quantitatively react the mono- and dialkylamines with the formyldialkanolamine to provide a reaction product comprising the trialkylamine, a formyldialkylamine, a formylmonoalkylamine, unreacted formyldialkanolamine and the corresponding dialkanolamine. The trialkylamine can be separated from the formylalkalamines by simple distillation and the formylamines can be separated from each other by vacuum distillation. Thereafter, each of the formylalkylamines is reacted with a formyldialkanolamine selected from the group consisting of formyldiethanolamine, formyl aminoethylethanolamine and formyl 2-(2-aminoethylamino)-ethanol at a temperature of about 120.degree. to about 140.degree. C. to provide a reaction product comprising the alkylamine and formyldialkanolamine. The alkylamine can be recovered from each of the reaction mixtures by simple distillation.
In accordance with another embodiment of the present invention, a dialkanolamine selected from the group consisting of diethanolamine, aminoethylethanolamine and 2-(2-aminoethylamino)-ethanol is brought into contact with at least an equimolar amount of carbon monoxide at a temperature of about 100.degree. to about 200.degree. C. and a pressure of about 700 to about 10,000 psig to substantially selectively convert the dialkanolamine to the corresponding formyldialkanolamine to form a reaction product that is useful as a starting material for the present invention, as illustrated by the following equation: ##STR1## The thus prepared formyldialkanolamine is added to an alkylamine mixture and heated at a temperature of about 120.degree. to about 160.degree. C. and a pressure of about 500 to about 3,000 psig to form a reaction product comprising trialkylamines and formyl derivatives of the dialkylamines together with unreacted formyldialkanolamine and the corresponding alkanolamine. Thereafter, the trialkylamine, the formyldialkylamine and the formylmonoalkylamine are separately recovered by distillation. The thus separated formyldialkylamine and formylmonoalkylamine can be reacted with an additional quantity of dialkanolamine to provide the dialkylamine and the monoalkylamine and formylalkanolamine.